My memory tells me we have seen this location before, but I can't remember how long ago, so not sure what the outrurn was. GSV 2024 shows two No Right Turn signs one each side of the road.
So, OP, why did you turn with those signs in place ? High-sided vehicles like buses perhaps. Two buses passing in each bus lane would have obscured the signs, so we need to see the video. TfL are in the dark ages IT-wise, to send out videos on DVDs.It would be quite easy for them to join with other London councils and put it on-line but clearly they are not willing to do so for some obscure reason.